Extreme ultraviolet mask and method of manufacturing the same

ABSTRACT

A method of manufacturing an extreme ultraviolet mask, including forming a multilayer Mo/Si stack including alternating Mo and Si layers over a first major surface of a mask substrate, and forming a capping layer over the multilayer Mo/Si stack. An absorber layer is formed on the capping layer, and a hard mask layer is formed over the absorber layer. The hard mask layer is patterned to form a hard mask layer pattern. The hard mask layer pattern is extended into the absorber layer to expose the capping layer and form a mask pattern. A border pattern is formed around the mask pattern. The border pattern is extended through the multilayer Mo/Si stack to expose the mask substrate and form a trench surrounding the mask pattern. A passivation layer is formed along sidewalls of the trench.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and incorporates by referenceU.S. Provisional Application 62/565,714 filed on Sep. 29, 2017 in itsentirety.

TECHNICAL FIELD

The present disclosure is related to extreme ultraviolet EUV masks andmethods of manufacturing the masks. In particular, the presentdisclosure is related to protection of black borders of the EUV maskfrom being damaged during manufacturing of the EUV mask.

BACKGROUND

In EUV photolithography, the EUV light rays emitted from a plasma arereflected off a collector mirror, directed toward a patterned EUV mask,and reflected off the mask onto the target substrate. An EUV reflectivemask includes a substrate, an EUV reflective multilayered structure, andan EUV absorbing layer (‘absorber’). The EUV absorbing layer ispatterned by etching and photolithographic techniques to expose theunderneath EUV reflecting layers for EUV photolithographic patterning ofdesired patterns on the target substrate while the EUV absorbing layersabsorb the EUV light rays so as not to pattern the target substrate inthe undesired regions. Therefore, the thickness of the EUV absorbinglayer, the thickness of each of the layers in the EUV reflectivemultilayered structure, surface roughness of the above layers, and thehomogeneity of the material properties throughout the layers, areextremely important to the quality of EUV light irradiating the targetsubstrate. In industrial practice, off-axis illumination or otherfactors can cause a shadow effect on the target substrate and variationsin the thickness of the EUV light absorbing layer can affect the properfunctioning of the combination of the EUV light absorbing layer and theEUV reflecting multi-layered structure.

A ‘black border’ is formed at the edge of the desired patterns of theEUV reflective mask to avoid over-exposure of the edge of the patterns.The ‘black border’ is a non-reflective trench of a sufficient depth fordestructive interference to solve the problem of shadow effect by makingthe borders non-reflecting (optically ‘black’). During the processing ofextreme ultraviolet masks, black borders can be damaged. Undercutetching of the silicon layers in the Mo/Si multilayer in the blackborder can occur because of the difference in etch selectivity of Mo andSi. Mo has a higher etch selectivity compared to Si. Hydrogen canpreferentially etch Si, undercutting the Mo layers. In addition, Monanocrystal aggregation can occur, forming spherical particles that cancontaminate the mask. An improved EUV mask and method of making EUVmasks is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 shows an extreme ultraviolet lithography tool according to anembodiment of the disclosure.

FIG. 2 shows a schematic diagram of a detail of an extreme ultravioletlithography tool according to an embodiment of the disclosure.

FIG. 3 shows a process stage of a method of manufacturing an EUV maskaccording to an embodiment of the present disclosure.

FIG. 4 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 5 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 6 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 7 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 8 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 9 shows a process stage of the method of manufacturing the EUV maskaccording to an embodiment of the present disclosure.

FIG. 10 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 11 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 12 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 13 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 14 shows a process stage of a method of manufacturing an EUV maskaccording to an embodiment of the present disclosure.

FIG. 15 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 16 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 17 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 18 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 19 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 20 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 21 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 22 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 23 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 24 shows a process stage of the method of manufacturing the EUVmask according to an embodiment of the present disclosure.

FIG. 25 shows a flowchart showing the methods of manufacturing an EUVmask according to embodiments of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“being made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

To address the trend of the Moore's law for decreasing size of chipcomponents and the demand of higher computing power chips for mobileelectronic devices such as smart phones with computer functions,multi-tasking capabilities, or even with workstation power. Smallerwavelength photolithography exposure systems are desirable. Extremeultraviolet (EUV) photolithography technique uses an EUV radiationsource to emit a EUV light ray with wavelength of 13.5 nm. Because thiswavelength is also in the x-ray radiation wavelength region, the EUVradiation source is also called a soft x-ray radiation source. The EUVlight rays are emitted from a laser-produced plasma (LPP) are collectedby a collector mirror and reflected toward a patterned mask.

FIG. 1 is a schematic view of an EUV lithography tool with an LPP-basedEUV radiation source, in accordance with some embodiments of the presentdisclosure. The EUV lithography system includes an EUV radiation source100 to generate EUV radiation, an exposure device 200, such as ascanner, and an excitation laser source 300. As shown in FIG. 1, in someembodiments, the EUV radiation source 100 and the exposure device 200are installed on a main floor MF of a clean room, while the excitationlaser source 300 is installed in a base floor BF located under the mainfloor. Each of the EUV radiation source 100 and the exposure device 200are placed over pedestal plates PP1 and PP2 via dampers DP1 and DP2,respectively. The EUV radiation source 100 and the exposure device 200are coupled to each other by a coupling mechanism, which may include afocusing unit.

The EUV lithography tool is designed to expose a resist layer to EUVlight (also interchangeably referred to herein as EUV radiation). Theresist layer is a material sensitive to the EUV light. The EUVlithography system employs the EUV radiation source 100 to generate EUVlight, such as EUV light having a wavelength ranging between about 1 nmand about 100 nm. In one particular example, the EUV radiation source100 generates an EUV light with a wavelength centered at about 13.5 nm.In the present embodiment, the EUV radiation source 100 utilizes amechanism of laser-produced plasma (LPP) to generate the EUV radiation.

The exposure device 200 includes various reflective optic components,such as convex/concave/flat mirrors, a mask holding mechanism includinga mask stage, and wafer holding mechanism. The EUV radiation EUVgenerated by the EUV radiation source 100 is guided by the reflectiveoptical components onto a mask secured on the mask stage. In someembodiments, the mask stage includes an electrostatic chuck (e-chuck) tosecure the mask.

FIG. 2 is a simplified schematic diagram of a detail of an extremeultraviolet lithography tool according to an embodiment of thedisclosure showing the exposure of photoresist coated substrate 210 witha patterned beam of EUV light. The exposure device 200 is an integratedcircuit lithography tool such as a stepper, scanner, step and scansystem, direct write system, device using a contact and/or proximitymask, etc., provided with one or more optics 205 a, 205 b, for example,to illuminate a patterning optic 205 c, such as a reticle, with a beamof EUV light, to produce a patterned beam, and one or more reductionprojection optics 205 d, 205 e, for projecting the patterned beam ontothe substrate 210. A mechanical assembly (not shown) may be provided forgenerating a controlled relative movement between the substrate 210 andpatterning optic 205 c. As further shown in FIG. 2, the EUVL toolincludes an EUV light source 100 including an EUV light radiator ZEemitting EUV light in a chamber 105 that is reflected by a collector 110along a path into the exposure device 200 to irradiate the substrate210.

As used herein, the term “optic” is meant to be broadly construed toinclude, and not necessarily be limited to, one or more components whichreflect and/or transmit and/or operate on incident light, and includes,but is not limited to, one or more lenses, windows, filters, wedges,prisms, grisms, gradings, transmission fibers, etalons, diffusers,homogenizers, detectors and other instrument components, apertures,axicons and mirrors including multi-layer mirrors, near-normal incidencemirrors, grazing incidence mirrors, specular reflectors, diffusereflectors and combinations thereof. Moreover, unless otherwisespecified, neither the term “optic”, as used herein, are meant to belimited to components which operate solely or to advantage within one ormore specific wavelength range(s) such as at the EUV output lightwavelength, the irradiation laser wavelength, a wavelength suitable formetrology or any other specific wavelength.

Because gas molecules absorb EUV light, the lithography system for theEUV lithography patterning is maintained in a vacuum or a-low pressureenvironment to avoid EUV intensity loss.

In the present disclosure, the terms mask, photomask, and reticle areused interchangeably. In the present embodiment, the patterning optic205 c is a reflective mask. In an embodiment, the reflective mask 205 cincludes a substrate with a suitable material, such as a low thermalexpansion material or fused quartz. In various examples, the materialincludes TiO₂ doped SiO₂, or other suitable materials with low thermalexpansion. The reflective mask 205 c includes multiple reflective layers(ML) deposited on the substrate. The ML includes a plurality of filmpairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer ofmolybdenum above or below a layer of silicon in each film pair).Alternatively, the ML may include molybdenum-beryllium (Mo/Be) filmpairs, or other suitable materials that are configured to highly reflectthe EUV light. The mask 205 c may further include a capping layer, suchas ruthenium (Ru), disposed on the ML for protection. The mask furtherincludes an absorption layer, such as a tantalum boron nitride (TaBN)layer, deposited over the ML. The absorption layer is patterned todefine a layer of an integrated circuit (IC). Alternatively, anotherreflective layer may be deposited over the ML and is patterned to definea layer of an integrated circuit, thereby forming an EUV phase shiftmask.

In various embodiments of the present disclosure, the photoresist coatedsubstrate 210 is a semiconductor wafer, such as a silicon wafer or othertype of wafer to be patterned.

The EUVL tool further include other modules or is integrated with (orcoupled with) other modules in some embodiments.

As shown in FIG. 1, the EUV radiation source 100 includes a targetdroplet generator 115 and a LPP collector 110, enclosed by a chamber105. In various embodiments, the target droplet generator 115 includes areservoir to hold a source material and a nozzle 120 through whichtarget droplets DP of the source material are supplied into the chamber105.

In some embodiments, the target droplets DP are droplets of tin (Sn),lithium (Li), or an alloy of Sn and Li. In some embodiments, the targetdroplets DP each have a diameter in a range from about 10 microns (μm)to about 100 μm. For example, in an embodiment, the target droplets DPare tin droplets, having a diameter of about 10 μm to about 100 μm. Inother embodiments, the target droplets DP are tin droplets having adiameter of about 25 μm to about 50 μm. In some embodiments, the targetdroplets DP are supplied through the nozzle 120 at a rate in a rangefrom about 50 droplets per second (i.e., an ejection-frequency of about50 Hz) to about 50,000 droplets per second (i.e., an ejection-frequencyof about 50 kHz).

Referring back to FIG. 1, an excitation laser LR2 generated by theexcitation laser source 300 is a pulse laser. The laser pulses LR2 aregenerated by the excitation laser source 300. The excitation lasersource 300 may include a laser generator 310, laser guide optics 320 anda focusing apparatus 330. In some embodiments, the laser source 310includes a carbon dioxide (CO₂) or a neodymium-doped yttrium aluminumgarnet (Nd:YAG) laser source with a wavelength in the infrared region ofthe electromagnetic spectrum. For example, the laser source 310 has awavelength of 9.4 μm or 10.6 μm, in an embodiment. The laser light LR1generated by the laser generator 300 is guided by the laser guide optics320 and focused into the excitation laser LR2 by the focusing apparatus330, and then introduced into the EUV radiation source 100.

In some embodiments, the excitation laser LR2 includes a pre-heat laserand a main laser. In such embodiments, the pre-heat laser pulse(interchangeably referred to herein as the “pre-pulse) is used to heat(or pre-heat) a given target droplet to create a low-density targetplume with multiple smaller droplets, which is subsequently heated (orreheated) by a pulse from the main laser, generating increased emissionof EUV light.

In various embodiments, the pre-heat laser pulses have a spot size about100 μm or less, and the main laser pulses have a spot size in a range ofabout 150 μm to about 300 μm. In some embodiments, the pre-heat laserand the main laser pulses have a pulse-duration in the range from about10 ns to about 50 ns, and a pulse-frequency in the range from about 1kHz to about 100 kHz. In various embodiments, the pre-heat laser and themain laser have an average power in the range from about 1 kilowatt (kW)to about 50 kW. The pulse-frequency of the excitation laser LR2 ismatched with the ejection-frequency of the target droplets DP in anembodiment.

The laser light LR2 is directed through windows (or lenses) into thezone of excitation ZE. The windows adopt a suitable materialsubstantially transparent to the laser beams. The generation of thepulse lasers is synchronized with the ejection of the target droplets DPthrough the nozzle 120. As the target droplets move through theexcitation zone, the pre-pulses heat the target droplets and transformthem into low-density target plumes. A delay between the pre-pulse andthe main pulse is controlled to allow the target plume to form and toexpand to an optimal size and geometry. In various embodiments, thepre-pulse and the main pulse have the same pulse-duration and peakpower. When the main pulse heats the target plume, a high-temperatureplasma is generated. The plasma emits EUV radiation EUV, which iscollected by the collector mirror 110. The collector 110 furtherreflects and focuses the EUV radiation for the lithography exposingprocesses performed through the exposure device 200. The droplet catcher125 is used for catching excessive target droplets. For example, sometarget droplets may be purposely missed by the laser pulses.

Referring back to FIG. 1, the collector 110 is designed with a propercoating material and shape to function as a mirror for EUV collection,reflection, and focusing. In some embodiments, the collector 110 isdesigned to have an ellipsoidal geometry. In some embodiments, thecoating material of the collector 100 is similar to the reflectivemultilayer of the EUV mask. In some examples, the coating material ofthe collector 110 includes a ML (such as a plurality of Mo/Si filmpairs) and may further include a capping layer (such as Ru) coated onthe ML to substantially reflect the EUV light. In some embodiments, thecollector 110 may further include a grating structure designed toeffectively scatter the laser beam directed onto the collector 110. Forexample, a silicon nitride layer is coated on the collector 110 and ispatterned to have a grating pattern.

In such an EUV radiation source, the plasma caused by the laserapplication creates physical debris, such as ions, gases and atoms ofthe droplet, as well as the desired EUV radiation. It is necessary toprevent the accumulation of material on the collector 110 and also toprevent physical debris exiting the chamber 105 and entering theexposure device 200.

As shown in FIG. 1, in the present embodiment, a buffer gas is suppliedfrom a first buffer gas supply 130 through the aperture in collector 110by which the pulse laser is delivered to the tin droplets. In someembodiments, the buffer gas is H₂, He, Ar, N or another inert gas. Incertain embodiments, H₂ used as H radicals generated by ionization ofthe buffer gas can be used for cleaning purposes. The buffer gas canalso be provided through one or more second buffer gas supplies 135toward the collector 110 and/or around the edges of the collector 110.Further, the chamber 105 includes one or more gas outlets 140 so thatthe buffer gas is exhausted outside the chamber 105.

Hydrogen gas has low absorption to the EUV radiation. Hydrogen gasreaching the coating surface of the collector 110 reacts chemically witha metal of the droplet forming a hydride, e.g., metal hydride. When tin(Sn) is used as the droplet, stannane (SnH₄), which is a gaseousbyproduct of the EUV generation process, is formed. The gaseous SnH₄ isthen pumped out through the outlet 140.

FIGS. 3-13 show a process of manufacturing an EUV mask according to anembodiment of the present disclosure. FIG. 3 shows an extremeultraviolet (EUV) mask blank according to an embodiment of the presentdisclosure. The EUV mask blank includes a multilayered stack 20 ofmolybdenum layers 17 and silicon layers 19 (‘Mo/Si stack 20’). The Mo/Sistack 20 includes alternating Mo layers 17 and Si layers 19 disposedover a first major surface of a mask substrate 10. A capping layer 25 isdisposed over the Mo/Si stack 20, and an EUV absorbing layer or absorber30 is disposed over the capping layer 25. An anti-reflection layer 35 isdisposed over the EUV absorbing layer 30. A hard mask layer 40 is formedover the EUV absorbing layer 30. A first photoresist layer 45 is formedover the hard mask layer 40.

In the embodiment shown in FIG. 3, a conductive backside coating layer15 is optionally deposited on the second major surface of the masksubstrate 10 opposite to the first major surface. The conductivebackside coating layer 15 is used to fix the mask for photolithographicoperation by electrostatic chucking in some embodiments. In anembodiment, the conductive layer 15 is formed of a ceramic compoundincluding chromium nitride or any suitable material for electrostaticchucking of the mask.

The mask substrate 10 is made of a low thermal expansion glass materialincluding titanium oxide doped silicon dioxide, or any other suitablelow thermal expansion materials such as quartz, silicon, siliconcarbide, black diamond, and/or other low thermal expansion substancesknown in the art that can minimize the image distortion due to maskheating in the EUV photolithographic environment, in some embodiments ofthe present disclosure. The mask substrate 10 has a low defect level,such as a high purity single crystal substrate, and a low level ofsurface roughness, as measured using an atomic force microscope.

The multilayered stack 20 of alternating Mo layers 17 and Si layers 19deposited over the mask substrate 10 provides Fresnel resonantreflections across the interfaces between the Mo layer and Si layer ofdifferent refractive indices by use of an appropriate thickness for eachlayer inside the multilayer in some embodiments of the presentdisclosure. High quality reflections rely on constructive interferenceby phase-matching and intensity adding-up of light rays reflected fromdifferent layers. The thickness of the layers depends on the wavelengthof the incident light and the angle of incidence to the EUV mask. For aspecific angle of incidence, the thickness of each of the layers of themultilayered stack 20 is chosen to achieve maximal constructiveinterference for light reflected at different interfaces of themultilayered stack 20. Thus, even thickness and low surface roughness ofeach of the layers in the multilayered stack 20 are required for highquality Fresnel resonant reflections. A thickness of each of the layersin the multilayered stack 20 is 5-7 nm in some embodiments of thepresent disclosure.

In some embodiments of the present disclosure, the multilayered stack 20includes alternating molybdenum layers 17 and beryllium layers 19. Insome embodiments of the present disclosure, the number of layers in themultilayered stack 20 is in a range from 20 to 100 although any numberof layers is allowed as long as sufficient reflectivity is maintainedfor imaging the target substrate. In some embodiments, the reflectivityis higher than about 70%. In some embodiments of the present disclosure,the Mo/Si multilayer stack 20 includes about 30 to about 60 alternatinglayers of Mo and Si. In other embodiments of the present disclosure, theMo/Si multilayer stack 20 includes about 40 to about 50 alternatinglayers each of Mo and Si.

Methods of forming the layers of the multilayered stack 20 includephysical vapor deposition (PVD) processes such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods such as a sol-gel method andmetal-organic decomposition; and/or any other suitable method known inthe art.

The capping layer 25 formed over the multilayered stack 20 preventsoxidation of the multilayered stack 20 in some embodiments. In someembodiments of the present disclosure, the capping layer 25 is formed ofa material including silicon and ruthenium. In some embodiments of thepresent disclosure, the capping layer 25 has a thickness of about 7 nm.Methods of forming the capping layer 25 include physical vapordeposition (PVD) processes such as evaporation, RF or DC sputtering;chemical vapor deposition (CVD) processes, such as atmospheric-pressure,low-pressure, plasma-enhanced, and high-density plasma CVD; atomic layerdeposition (ALD); ion beam deposition; and liquid-phase non-vacuummethods, such as a sol-gel method and a metal-organic decomposition;and/or any other suitable method known in the art.

The EUV absorbing layer or absorber 30 formed over the capping layer 25absorbs radiation with wavelength in a range of EUV wavelengths. The EUVabsorbing layer 30 is formed of a single layer or multiple layers insome embodiments of the present disclosure. In some embodiments of thepresent disclosure, the EUV absorbing layer 30 is formed of a materialincluding a tantalum compound. In some embodiments of the presentdisclosure, the EUV absorbing layer 30 is made of TaN or TaBN. In someembodiments of the present disclosure, the material used to make the EUVabsorbing layer 30 also includes molybdenum, palladium, zirconium,nickel silicide, titanium, titanium nitride, chromium, chromium oxide,aluminum oxide, aluminum-copper alloy, or other suitable materials. Thethickness of the EUV absorbing layer 30 is not limited as long as theoverall reflectivity of the EUV mask is more than 70%.

Methods of forming the EUV absorbing layer or absorber 30 includephysical vapor deposition (PVD) processes, such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods, such as a sol-gel method and ametal-organic decomposition, and/or any other suitable method known inthe art.

The anti-reflection layer 35 disposed over the EUV absorbing layer 30 isformed of a material including SiO₂, SiN, TaBO, TaO₅, Cr₂O₃, ITO (indiumtin oxide), or any suitable material, in some embodiments of the presentdisclosure. The anti-reflection layer 35 reduces reflections ofphotolithographic radiation. Methods of forming the anti-reflectionlayer 35 include physical vapor deposition (PVD) processes, such asevaporation, RF or DC sputtering; chemical vapor deposition (CVD)processes such as atmospheric-pressure, low-pressure, plasma-enhanced,and high-density plasma CVD; atomic layer deposition (ALD); ion beamdeposition; and liquid-phase non-vacuum methods, such as a sol-gelmethod and a metal-organic decomposition; and/or any other suitablemethod known in the art.

The hard mask layer 40 formed over the anti-reflection layer 35 isformed of a material including silicon nitride in some embodiments ofthe present disclosure. Methods of forming the hard mask layer 40include physical vapor deposition (PVD) processes, such as evaporation,RF or DC sputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods, such as a sol-gel method and ametal-organic decomposition, and/or any other suitable method known inthe art.

The first photoresist layer 45 formed over the hard mask layer 40 isformed of a material including a photosensitive resist coating material.The first photoresist layer 45 is coated onto the hard mask layer 40 bya spin coating technique followed by baking in some embodiments.

FIG. 4 shows the formation of a pattern in the first photoresist layer45. After formation of the embodiment in FIG. 3, the first photoresistlayer 45 is subsequently patterned using photolithographic techniques toform a photoresist pattern 50, as shown in FIG. 4. The photoresistpattern 50 is extended into hard mask layer 40 to form a hard mask layerpattern 50′ using suitable etching techniques such as a dry etch, a wetetch, or a combination of the dry etch with the wet etch, as shown inFIG. 5. Next, as shown in FIG. 6, the hard mask layer pattern 50′ isextended through the anti-reflection layer 35 and EUV absorbing layer 30using suitable etching techniques such as a dry etch, a wet etch, or acombination of the dry etch and the wet etch exposing the capping layer25 and forming mask pattern 50″, and the photoresist pattern 50 isremoved as shown in FIG. 6.

As shown in FIG. 7, the hard mask layer 40 is subsequently removed insome embodiments using suitable etching techniques such as a dry etch, awet etch, or a combination of the dry etch with the wet etch.

A second photoresist layer 55 is subsequently formed over the maskpattern 50″ and the anti-reflection layer 35, as shown in FIG. 8. Thesecond photoresist layer 55 is selectively exposed to actinic radiationto form a latent pattern 60 surrounding the mask pattern in the secondphotoresist layer, as shown in FIG. 9. In some embodiments, the secondphotoresist layer 55 is a positive photoresist.

In FIG. 10, the second photoresist layer is developed forming a borderpattern 70 in the second photoresist layer 55. The border pattern 70 issubsequently extended through the anti-reflection layer 35, absorberlayer 30, capping layer 25, Mo/Si multilayer stack 20 using suitableetching techniques such as a dry etch, a wet etch, or a combination ofthe dry etch and the wet etch to expose portions of the mask substrate10, thereby forming a trench 70′ (called ‘black border’ or ‘black bordertrench’) surrounding the mask pattern, as shown in FIG. 11.

Next as shown in FIG. 12, the second photoresist layer 55 is removedusing a suitable photoresist stripping technique. The trench 70′ (blackborder) is formed in the multilayered Mo/Si stack 20 surrounding themask pattern 50″ using suitable etching techniques and a passivationlayer 75 is subsequently disposed along sidewalls of the trench 70′, asshown in FIG. 13. The passivation layer 75 subsequently formed alongsidewalls of the trench 70′ and over the mask pattern 50″ protects themask pattern 50″ and sidewalls of the Mo/Si multilayer stack 20 fromdefects and damage during processes performed subsequent to theformation of the passivation layer 75.

In some embodiments of the present disclosure, the forming of thepassivation layer 75 is formed by exposing the sidewalls of the trenchto a nitrogen-based gas. In some embodiments, the nitrogen-based gas isselected from the group consisting of N₂, NH₃, N₂H₂, and NO₂. In someembodiments, nitrogen-based plasma is used to form the passivationlayer. In some embodiments, forming the passivation layer comprises asol-gel process or a photochemical reaction.

In some embodiments of the present disclosure, the passivation layer 75includes a high-k material. In other embodiments of the presentdisclosure, the passivation layer 75 includes a material with highultraviolet absorbance, including nickel and cobalt. In some embodimentsof the present disclosure, the passivation layer 75 is made of siliconnitride, silicon oxynitride, or a metal doped silicon nitride. In someembodiments of the present disclosure, the passivation layer has athickness of less than about 10 nm.

FIGS. 14-24 show a process of manufacturing an EUV mask according toanother embodiment of the present disclosure. FIG. 14 shows an extremeultraviolet (EUV) mask blank according to an embodiment of the presentdisclosure. The EUV mask blank includes a multilayered stack 20 ofmolybdenum layers 17 and silicon layers 19 (‘Mo/Si stack 20’). The Mo/Sistack 20 includes alternating Mo layers 17 and Si layers 19 disposedover a first major surface of a mask substrate 10. A capping layer 25 isdisposed over the Mo/Si stack 20, and an EUV absorbing layer or absorber30 is disposed over the capping layer 25. An anti-reflection layer 35 isdisposed over the EUV absorbing layer 30. A hard mask layer 40 is formedover the EUV absorbing layer 30. A first photoresist layer 45 is formedover the hard mask layer 40.

In the embodiment shown in FIG. 14, a conductive backside coating layer15 is optionally deposited on the second major surface of the masksubstrate 10 opposite to the first major surface. The conductivebackside coating layer 15 is used to fix the mask for photolithographicoperation by electrostatic chucking in some embodiments. In anembodiment, the conductive layer 15 is formed of a ceramic compoundincluding chromium nitride or any suitable material for electrostaticchucking of the mask.

The mask substrate 10 is made of a low thermal expansion glass materialincluding titanium oxide doped silicon dioxide, or any other suitablelow thermal expansion materials such as quartz, silicon, siliconcarbide, black diamond, and/or other low thermal expansion substancesknown in the art that can minimize the image distortion due to maskheating in the EUV photolithographic environment, in some embodiments ofthe present disclosure. The mask substrate 10 has a low defect level,such as a high purity single crystal substrate, and a low level ofsurface roughness, as measured using an atomic force microscope.

The multilayered stack 20 of alternating Mo layers 17 and Si layers 19deposited over the mask substrate 10 provides Fresnel resonantreflections across the interfaces between the Mo layer and Si layer ofdifferent refractive indices by use of an appropriate thickness for eachlayer inside the multilayer in some embodiments of the presentdisclosure. High quality reflections rely on constructive interferenceby phase-matching and intensity adding-up of light rays reflected fromdifferent layers. The thickness of the layers depends on the wavelengthof the incident light and the angle of incidence to the EUV mask. For aspecific angle of incidence, the thickness of each of the layers of themultilayered stack 20 is chosen to achieve maximal constructiveinterference for light reflected at different interfaces of themultilayered stack 20. Thus, even thickness and low surface roughness ofeach of the layers in the multilayered stack 20 are required for highquality Fresnel resonant reflections. A thickness of each of the layersin the multilayered stack 20 is 5-7 nm in some embodiments of thepresent disclosure.

In some embodiments of the present disclosure, the multilayered stack 20includes alternating molybdenum layers 17 and beryllium layers 19. Insome embodiments of the present disclosure, the number of layers in themultilayered stack 20 is in a range from 20 to 100 although any numberof layers is allowed as long as sufficient reflectivity is maintainedfor imaging the target substrate. In some embodiments, the reflectivityis higher than about 70%. In some embodiments of the present disclosure,the Mo/Si multilayer stack 20 includes about 30 to about 60 alternatinglayers of Mo and Si. In other embodiments of the present disclosure, theMo/Si multilayer stack 20 includes about 40 to about 50 alternatinglayers each of Mo and Si The method to form the layers of themultilayered stack 20 includes physical vapor deposition (PVD) processessuch as evaporation, RF or DC sputtering; chemical vapor deposition(CVD) processes, such as atmospheric-pressure, low-pressure,plasma-enhanced, and high-density plasma CVD; atomic layer deposition(ALD); ion beam deposition; and liquid-phase non-vacuum methods such asa sol-gel method and metal-organic decomposition; and/or any othersuitable method known in the art.

The capping layer 25 formed over the multilayered stack 20 preventsoxidation of the multilayered stack 20 in some embodiments. In someembodiments of the present disclosure, the capping layer 25 is formed ofa material including silicon and ruthenium. In some embodiments of thepresent disclosure, the capping layer 25 has a thickness of about 7 nm.The method to form the capping layer 25 includes physical vapordeposition (PVD) processes such as evaporation, RF or DC sputtering;chemical vapor deposition (CVD) processes, such as atmospheric-pressure,low-pressure, plasma-enhanced, and high-density plasma CVD; atomic layerdeposition (ALD); ion beam deposition; and liquid-phase non-vacuummethods such as a sol-gel method and metal-organic decomposition; and/orany other suitable method known in the art.

The EUV absorbing layer or absorber 30 formed over the capping layer 25absorbs radiation with wavelength in a range of EUV wavelengths. The EUVabsorbing layer 30 is formed of a single layer or multiple layers insome embodiments of the present disclosure. In some embodiments of thepresent disclosure, the EUV absorbing layer 30 is formed of a materialincluding a tantalum compound. In some embodiments of the presentdisclosure, the EUV absorbing layer 30 is made of TaN or TaBN. In someembodiments of the present disclosure, the material used to make the EUVabsorbing layer 30 also includes molybdenum, palladium, zirconium,nickel silicide, titanium, titanium nitride, chromium, chromium oxide,aluminum oxide, aluminum-copper alloy, or other suitable materials. Thethickness of the EUV absorbing layer 30 is not limited as long as theoverall reflectivity of the EUV mask is more than 70%.

The method to form the EUV absorbing layer or absorber 30 includesphysical vapor deposition (PVD) processes such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods such as a sol-gel method andmetal-organic decomposition; and/or any other suitable method known inthe art.

The anti-reflection layer 35 disposed over the EUV absorbing layer 30 isformed of a material including SiO₂, SiN, TaBO, TaO₅, Cr₂O₃, ITO, or anysuitable material, in some embodiments of the present disclosure. Theanti-reflection layer 35 reduces reflection of lithographic radiation.The method to form the anti-reflection layer 35 includes physical vapordeposition (PVD) processes such as evaporation, RF or DC sputtering;chemical vapor deposition (CVD) processes, such as atmospheric-pressure,low-pressure, plasma-enhanced, and high-density plasma CVD; atomic layerdeposition (ALD); ion beam deposition; and liquid-phase non-vacuummethods such as a sol-gel method and metal-organic decomposition; and/orany other suitable method known in the art.

The hard mask layer 40 formed over the anti-reflection layer 35 isformed of a material including silicon nitride in some embodiments ofthe present disclosure. The method to form the hard mask layer 40includes physical vapor deposition (PVD) processes such as evaporation,RF or DC sputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods such as a sol-gel method andmetal-organic decomposition; and/or any other suitable method known inthe art.

The first photoresist layer 45 formed over the hard mask layer 40 isformed of a material including a photosensitive resist coating material.The first photoresist layer 45 is coated onto the hard mask layer 40 bya spin coating technique followed by baking in some embodiments.

FIG. 15 shows the formation of a pattern in the first photoresist layer45. After formation of the embodiment in FIG. 14, the first photoresistlayer 45 is subsequently patterned using photolithographic techniques toform a photoresist pattern 50, as shown in FIG. 15. The photoresistpattern 50 is extended into hard mask layer 40 to form a hard mask layerpattern 50′ using suitable etching techniques such as a dry etch, a wetetch, or a combination of the dry etch and the wet etch, as shown inFIG. 16.

Next, as shown in FIG. 17, the hard mask layer pattern 50′ is extendedthrough the anti-reflection layer 35 and EUV absorbing layer 30 usingsuitable etching techniques such as a dry etch, a wet etch, or acombination of the dry etch and the wet etch exposing the capping layer25 and forming mask pattern 50″, and the photoresist pattern 50 isremoved as shown in FIG. 17. As shown in FIG. 18, the hard mask layer 40is subsequently removed in some embodiments using suitable etchingtechniques such as a dry etch, a wet etch, or a combination of the dryetch and the wet etch.

A second photoresist layer 55 is subsequently formed over the maskpattern 50″ and the anti-reflection layer 35, as shown in FIG. 19. Thesecond photoresist layer 55 is selectively exposed to actinic radiationto form a latent pattern 60 surrounding the mask pattern in the secondphotoresist layer, as shown in FIG. 20. In some embodiments, the secondphotoresist layer 55 is a positive photoresist.

In FIG. 21, the second photoresist layer is developed forming a borderpattern 70 in the second photoresist layer 55. The border pattern 70 issubsequently extended through the anti-reflection layer 35, absorberlayer 30, capping layer 25, Mo/Si multilayer stack 20 using suitableetching techniques such as a dry etch, a wet etch, or a combination ofthe dry etch and the wet etch to expose portions of the mask substrate10, thereby forming a trench 70′ (called ‘black border’ or ‘black bordertrench’) surrounding the mask pattern, as shown in FIG. 22.

Next as shown in FIG. 23, a passivation layer 75 is subsequentlydisposed along sidewalls of the trench 70′. The passivation layer 75formed along sidewalls of the trench 70′ and over the mask pattern 50″protects the mask pattern 50″ using suitable etching techniques andsidewalls of the Mo/Si multilayer stack 20 from defects and damageduring subsequent processing.

Subsequently, the second photoresist layer 55 is removed using asuitable photoresist stripping technique (FIG. 24). After the secondphotoresist removal, at least a portion of the passivation layer 75remains along the trench 70′ sidewalls (FIG. 24).

In some embodiments of the present disclosure, the forming of thepassivation layer 75 is formed by exposing the sidewalls of the trenchto a nitrogen-based gas. In some embodiments, the nitrogen-based gas isselected from the group consisting of N₂, NH₃, N₂H₂, and NO₂. In someembodiments, nitrogen-based plasma is used to form the passivationlayer. In some embodiments, forming the passivation layer comprises asol-gel process or a photochemical reaction.

In some embodiments of the present disclosure, the passivation layer 75includes a high-k material. In other embodiments of the presentdisclosure, the passivation layer 75 includes a material with highultraviolet absorbance, including nickel and cobalt. In some embodimentsof the present disclosure, the passivation layer 75 is made of siliconnitride, silicon oxynitride, or a metal doped silicon nitride. In someembodiments of the present disclosure, the passivation layer has athickness of less than about 10 nm.

FIG. 25 shows a flowchart showing methods of manufacturing an EUV maskaccording to the embodiments shown in FIGS. 3-13 and FIGS. 14-24. InFIG. 25, step S2501 includes a process of forming a multilayered stackof molybdenum layer and silicon layer (also called ‘Mo/Si stack’). TheMo/Si stack includes alternating Mo layers and Si layers disposed over afirst major surface of a mask substrate. A capping layer is disposedover the Mo/Si stack, and an EUV absorbing layer or absorber is disposedover the capping layer. An anti-reflection layer is disposed over theEUV absorbing layer. A hard mask layer is formed over the EUV absorbinglayer. A first photoresist layer is formed over the hard mask layer. Themultilayered stack of molybdenum layer and silicon layer is formed usingphysical vapor deposition (PVD) processes such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods such as a sol-gel method andmetal-organic decomposition; and/or any other suitable method known inthe art.

After step S2501, step 2502 is carried out to pattern the firstphotoresist layer using photolithographic techniques to form aphotoresist pattern.

After step S2502, step S2503 is carried out to extend the photoresistpattern into the hard mask layer to form a hard mask layer pattern usingsuitable etching techniques such as a dry etch, a wet etch, or acombination of the dry etch and the wet etch.

After step S2503, step S2504 is carried out to extend the hard masklayer pattern through the anti-reflection layer and EUV absorbing layerusing suitable etching techniques such as a dry etch, a wet etch, or acombination of the dry etch with the wet etch, thereby exposing thecapping layer and forming mask pattern, and the photoresist pattern isremoved.

After step S2504, step 2505 is carried out to remove the hard mask layerusing suitable etching techniques such as dry etch or wet etch or acombination of the dry etch and the wet etch.

After step S2505, step 2506 is carried out to form a second photoresistlayer over the mask pattern and the anti-reflection layer.

After step S2506, step 2507 is carried out to selectively expose thesecond photoresist layer to actinic radiation to form a latent patternsurrounding the mask pattern in the second photoresist layer. In someembodiments, the second photoresist layer is a positive photoresist.

After step S2507, step 2508 is carried out to develop the secondphotoresist layer to form a border pattern in the second photoresistlayer.

After step S2508, step 2509 is carried out to extend the border patternthrough the anti-reflection layer, absorber layer, capping layer, Mo/Simultilayer stack using suitable etching techniques such as a dry etch orwet etch or a combination of the dry etch with the wet etch to exposeportions of the mask substrate, thereby forming a trench (‘black border’or ‘black border trench’) surrounding the mask pattern.

In some embodiments, after step S2509, step 2510(a) is carried out toremove the second photoresist layer using a suitable photoresiststripping technique.

After step S2510(a), step 2511(a) is carried out to form the trench(black border) is formed in the multilayered Mo/Si stack surrounding themask pattern, and a passivation layer is subsequently disposed alongsidewalls of the trench. The passivation layer subsequently formed alongsidewalls of the trench and over the mask pattern protects the maskpattern and sidewalls of the Mo/Si multilayer stack from defects anddamage during processes performed subsequent to the formation of thepassivation layer.

Alternatively, in another embodiment, after step S2509, step 2510(b) iscarried out to form the trench (black border) in the multilayered Mo/Sistack surrounding the mask pattern, and a passivation layer issubsequently disposed along sidewalls of the trench. The passivationlayer subsequently formed along sidewalls of the trench and over themask pattern protects the mask pattern and sidewalls of the Mo/Simultilayer stack from defects and damage during processes performedsubsequent to the formation of the passivation layer.

After step S2510(b), step 2511(b) is carried out to remove the secondphotoresist layer using a suitable photoresist stripping technique.After the second photoresist removal, at least a portion of thepassivation layer remains along the trench sidewalls.

Embodiments of the present disclosure prevent black border defectissues, such as those caused by undercut etching of the silicon layers.In addition, embodiments of the present disclosure prevent the formationof spherical Mo particles. The passivation layer 75 is formed alongblack border sidewalls to protect the exposed edges of the Mo and Silayers. For example, in some embodiments, Si—N bonds are formed duringthe formation of the passivation layer. The Si—N bonds can preventhydrogen radical etching of the silicon.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to an embodiment of the present disclosure, a method ofmanufacturing an extreme ultraviolet mask, includes forming a multilayerMo/Si stack including alternating Mo and Si layers over a first majorsurface of a mask substrate, and forming a capping layer over themultilayer Mo/Si stack. An absorber layer is formed on the cappinglayer, a hard mask layer is formed over the absorber layer. The hardmask layer is patterned to form a hard mask layer pattern. The hard masklayer pattern is extended into the absorber layer to expose the cappinglayer and form a mask pattern. A border pattern is formed around themask pattern. The border pattern is extended through the multilayerMo/Si stack to expose the mask substrate and form a trench surroundingthe mask pattern. A passivation layer is formed along sidewalls of thetrench. In some embodiments of the present disclosure, the methodincludes forming a conductive backside coating layer over a second majorsurface of the mask substrate opposing the first major surface. In someembodiments of the present disclosure, the method includes forming ananti-reflection layer over the absorber layer. In some embodiments ofthe present disclosure, the method includes removing the hard mask layerafter forming the mask pattern. In some embodiments of the presentdisclosure, the method includes forming a first photoresist layer overthe hard mask layer. In some embodiments of the present disclosure, themethod includes forming a second photoresist layer over the absorberlayer and the mask pattern. In some embodiments of the presentdisclosure, the forming a passivation layer includes exposing thesidewalls of the trench to a nitrogen-based gas selected from the groupconsisting of N₂, NH₃, N₂H₂, and NO₂.

According to another embodiment of the present disclosure, a method ofmanufacturing an extreme ultraviolet mask, includes patterning anabsorber layer disposed over a multilayer Mo/Si stack includingalternating Mo and Si layers disposed over a first major surface of amask substrate to form a mask pattern. A border pattern is formed aroundthe mask pattern. The border pattern is extended through the multilayerMo/Si stack to expose the mask substrate and form a trench surroundingthe mask pattern. A passivation layer is formed over the mask patternand along sidewalls of the trench. In some embodiments of the presentdisclosure, the method includes forming a capping layer over the Mo/Sistack. In some embodiments of the present disclosure, the methodincludes forming a hard mask layer over the absorber layer, patterningthe hard mask layer to form a hard mask layer pattern, and extending thehard mask layer pattern into the absorber layer to form the maskpattern. In some embodiments of the present disclosure, the methodincludes forming a photoresist layer over the absorber layer and themask pattern. In some embodiments of the present disclosure, the methodincludes removing the photoresist layer before forming the passivationlayer. In some embodiments of the present disclosure, the passivationlayer is formed over the photoresist layer. In some embodiments of thepresent disclosure, the forming the passivation layer includes exposingthe sidewalls of the trench and the mask pattern to a nitrogen-based gasselected from the group consisting of N₂, NH₃, N₂H₂, and NO₂.

According to another embodiment of the present disclosure, an extremeultraviolet mask, includes a multilayer Mo/Si stack includingalternating Mo and Si layers disposed over a first major surface of amask substrate. A capping layer is disposed over the Mo/Si stack, and anabsorber layer is disposed over the capping layer. A mask pattern isformed in the absorber layer. A trench formed in the multilayer Mo/Sistack surrounds the mask pattern, and a passivation layer is disposedalong sidewalls of the trench. In some embodiments of the presentdisclosure, the extreme ultraviolet mask further includes ananti-reflection layer disposed over the absorber layer. In someembodiments of the present disclosure, the passivation layer is made ofa silicon nitride, a silicon oxynitride, or a metal doped siliconnitride. In some embodiments of the present disclosure, the passivationlayer has a thickness of less than about 10 nm. In some embodiments ofthe present disclosure, the passivation layer includes a high-kmaterial. In some embodiments of the present disclosure, the passivationlayer includes nickel or cobalt.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of manufacturing an extreme ultravioletmask, comprising: forming a multilayer Mo/Si stack comprisingalternating Mo and Si layers over a first major surface of a masksubstrate made of a glass material; forming a capping layer over themultilayer Mo/Si stack; forming an absorber layer on the capping layer;forming a hard mask layer over the absorber layer; patterning the hardmask layer to form a hard mask layer pattern; extending the hard masklayer pattern into the absorber layer to expose the capping layer andforming a mask pattern; forming a border pattern around the maskpattern; extending the border pattern through the multilayer Mo/Si stackto expose the first major surface of the mask substrate and forming atrench surrounding the mask pattern; and forming a passivation layeralong sidewalls of the trench and in direct contact with the first majorsurface of the mask substrate.
 2. The method according to claim 1,further comprising forming a conductive backside coating layer over asecond major surface of the mask substrate opposing the first majorsurface.
 3. The method according to claim 1, further comprising formingan anti-reflection layer over the absorber layer.
 4. The methodaccording to claim 1, further comprising removing the hard mask layerafter forming the mask pattern.
 5. The method according to claim 1,further comprising forming a first photoresist layer over the hard masklayer.
 6. The method according to claim 5, further comprising forming asecond photoresist layer over the absorber layer and the mask pattern.7. The method according to claim 1, wherein the forming a passivationlayer comprises exposing the sidewalls of the trench to a nitrogen-basedgas selected from the group consisting of N₂, NH₃, N₂H₂, and NO₂.
 8. Amethod of manufacturing an extreme ultraviolet mask, comprising:patterning an absorber layer disposed over a multilayer Mo/Si stackcomprising alternating Mo and Si layers disposed over a first majorsurface of a mask substrate made of a glass material to form a maskpattern; forming a border pattern around the mask pattern; extending theborder pattern through the multilayer Mo/Si stack to expose the firstmajor surface of the mask substrate and forming a trench surrounding themask pattern; and forming a passivation layer over the mask pattern,along sidewalls of the trench, and in direct contact with the firstmajor surface of the mask substrate.
 9. The method according to claim 8,further comprising forming a capping layer over the Mo/Si stack.
 10. Themethod according to claim 9, further comprising forming a hard masklayer over the absorber layer; patterning the hard mask layer to form ahard mask layer pattern; and extending the hard mask layer pattern intothe absorber layer to form the mask pattern.
 11. The method according toclaim 10, further comprising forming a photoresist layer over theabsorber layer and the mask pattern.
 12. The method according to claim11, further comprising removing the photoresist layer before forming thepassivation layer.
 13. The method according to claim 11, wherein thepassivation layer is formed over the photoresist layer.
 14. The methodaccording to claim 8, wherein the forming the passivation layercomprises exposing the sidewalls of the trench and the mask pattern to anitrogen-based gas selected from the group consisting of N₂, NH₃, N₂H₂,and NO₂.
 15. An extreme ultraviolet mask, comprising: a multilayer Mo/Sistack comprising alternating Mo and Si layers disposed over a firstmajor surface of a mask substrate made of a glass material; a cappinglayer disposed over the Mo/Si stack; an absorber layer disposed over thecapping layer; a mask pattern formed in the absorber layer; a trenchformed in the multilayer Mo/Si stack surrounding the mask pattern, thetrench exposing the first major surface of the mask substrate; and apassivation layer disposed along sidewalls of the trench and in directcontact with the first major surface of the mask substrate.
 16. Theextreme ultraviolet mask according to claim 15, further comprising ananti-reflection layer disposed over the absorber layer.
 17. The extremeultraviolet mask according to claim 15, wherein the passivation layer ismade of a silicon nitride, a silicon oxynitride, a metal doped siliconnitride, or a composite including at least one of metal silicide, metalnitride and metal oxide.
 18. The extreme ultraviolet mask according toclaim 15, wherein the passivation layer has a thickness of less thanabout 10 nm.
 19. The extreme ultraviolet mask according to claim 15,wherein the passivation layer comprises a high-k material.
 20. Theextreme ultraviolet mask according to claim 15, wherein the passivationlayer comprises nickel or cobalt.